Chapter 4: Motherboards^75
The IBM PC AT
IBM next introduced its 16-bit PC AT (Advanced Technology) that included enough
additional circuitry that its motherboard (and case) was expanded in size. It was also the
size,shape,andmountingplacementsoftheAT’scasethatwaschosenbyclonemanufac-
turers for their XT-upgrade motherboards. The popularity of the AT established it as the
first real motherboard form factor standard.The Baby AT Form Factor
Following the success of the IBM PC AT, clone manufacturers began releasing their own
16-bitPCs.Higherintegrationtechnologyreducedthespacerequiredbysupportchipsets
and circuits allowing for a smaller motherboard. This smaller motherboard, which
trimmed3.5inchesoffthewidthandasmuchastwoinchesofftheheight,becameknown
as the Baby AT, shown in Figure 4-1. The Baby AT, so called because it would mount in
AT cases using the AT form factor’s mountings, became very popular because of its flexi-
bility and quickly surpassed the AT as the form factor of choice. Most of the computer
cases manufactured between 1984 and 1996 were Baby AT form factors.Figure 4-1. The Baby AT motherboard